Xerographic belt loading apparatus



Dec. 29, 1959 E. c. RICKER ,9

XEROGRAPHIC BELT LOADING APPARATUS Original Filed Feb. 18, 1955COMPRESSED 6A5 SUPPLY III INVENTOR. EUGENE C. RICKER.

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United States Patent XEROGRAPHIC BELT LOADING APPARATUS Originalapplication February 18, 1955, Serial No. 489,250. Divided and thisapplication February 18, 1957, Serial No. 640,930

2 Claims.

This invention relates in general to xerography and in particular todevelopment of electrostatic charge patterns and is a division of mypatent application Serial No. 489,250, filed February 18, 1955.

Xerography uses the physical phenomena of photoconductivity andelectrostatic attraction of electrostatically charged bodies to converta light image into a physical image consisting of, for instance, blackpowder on white paper. The xerographic plate consists of a film of aphotoconductive insulating material on a conductive backing member. Inuse, the plate is given an electrostatic surface charge and then exposedto a light image, which results in an electrostatic image on the platesurface. This electrostatic image, which may be allowed to remain on theplate or which may be transferred, is developed by allowing it toattract and collect electrically charged particles of powder. The powderimage may then be transferred and fixed to another surface, usually asheet of paper, and the plate may be cleaned for reuse, or the powderimage may be allowed to remain on the plate for photographing, viewing,or the like.

One method of image development is known as powder cloud development,and is described, for example, in Carlson US. Patent 2,221,776. In thistechnique of development, a dispersion of powder particles in gas ispassed to the surface area bearing the electrical image and properlycharged particles are drawn out of the cloud to form a powder depositionin electrical image configuration.

It is an object of this invention to improve upon means and methods forthe powder cloud development of electrostatic latent images.

It is also an object of this invention to improve upon apparatus forpowder cloud development of electrostatic latent images.

An object in the art of xerography, as in any art concerned with imagereproduction, is that of uniformly developing high quality copy. Meansof obtaining this objective while using powder cloud development isthrough the uniform and constant presentation to the electrostaticcharge pattern on a surface of a powder cloud of fine developer powderparticles uniformly and densely dispersed throughout.

Powder clouds of uniform and dense dispersion of powder particles may begenerated by passing a tape or belt of cloth or the like which has beenuniformly loaded with powder particles over an output tube at a uniformrate. Particles are blown from the belt or tape in a controlled gasstream, thereby producing a controlled aerosol of uniformly constant anddense dispersions of powder particles. This invention is concerned withthe uniform loading of belts, ribbons, and tapes with powder particlesand also the end product or the uniformly loaded or impregnated belt,ribbon, or tape of material.

It is, therefore, an object of this invention .todevise f ce new meansand methods for impregnating tapes or belts of material with xerographicdeveloper powder particles.

It is yet another object of this invention to devise apparatus foruniformly impregnating belts or tapes of material.

It is still further an object of this invention to devise a new product,a belt, ribbon, or tape of material im pregnated with xerographicdeveloper powder particles.

For a better understanding of this invention, together with otherfurther objects thereof, reference is now had to the followingdescription taken in connection with the accompanying drawings, and thescope of the invention will be pointed out in the appended claims.

Figure 1 is an isometric view of an embodiment of a belt, ribbon, ortape stretched between spools.

Figure 2 is a diagrammatic view' partially in section of an embodimentof a combination aerosol generator and tape loader.

Figure 3 is a diagrammatic view partially in section of anotherembodiment of a tape loading device.

For a more thorough discussion of this invention, reference is now hadto Figure 1 wherein is shown in detail an embodiment of a belt, ribbon,or tape according to this invention. As appears in this figure, thebelt, ribbon, or tape 11 stretches between spool 12 and spool 13. It isto be realized that the object of this invention is the loading of beltsand the loaded belt and there is no intent to limit this invention tobelts stretched between spools, as shown in this figure.

The belt 11 may be loaded or impregnated with xerographic developerpowder particles across its entire width, or it may be impregnated orloaded with developer powder particles only across a portion of itswidth.

An impregnated belt on spools as shown in this figure may be useddirectly in belt powder cloud generator devices simply by inserting thespools in their proper places in the apparatus and operating theequipment. During operation the belt will move at a uniform rate over anoutput tube and a constant, steady flow of gas will cause removal of theparticles in the belt into a gas stream, thereby creating an aerosol ofpowder particles. The aerosol may then be conveyed to the developmentzone for deposition of the powder particles on an electric chargepattern bearing surface. Before deposition, the particles of the aerosolmay be charged or deagglomerated, or both, in order to bring about finegrain xerographic development.

Belts may be impregnated with xerographic developer powder particles bybrushing the powder by hand into or against the belt, or they may beloaded or impregnated by tumbling the powder over the belt material andscraping off excess powder with a'blade or the like. Another techniquefor loading the belt is that of loading the powder into the materialwith a spatula or pressing the powder into the material between twosurfaces. In the brushing technique, the material is placed on a solidsupport and large quantities of powder are brushed over the material inall directions with a soft bristled brush. Excess powder is removed byshaking the belt.

Manual techniques for impregnating belts are satis factory for someapplications of loaded belts. For high quality xerographic development,however, it is desirable to eliminate the variables and human elementsof error which are present with these techniques. This may beaccomplished by using an automatic loading machine in which a uniformaerosol is directed at the belt material as the belt or tape moves at auniform speed through the aerosol.

Reference is now had to Figure 2 wherein is shown an embodiment of acombination device for automatic particles.

loading of belts. The elements of this combination aspirator type pickuptube 18, a tube to supply compressed gas to create aspiration ofparticles from disc 16 at pickup tube 18, drive means comprising a motor21 connected to the base of the grooved disc 16 by axle 22 which causesrotation of disc 16 through a gear wheel positioned against the gearwheel of the axle of disc 16. A supply of compressed gas is carried tothe equipment through input tube 23 and then through regulating valve'25 to tube 20. As shown, tube 20 carries the compressed gas fromregulating valve 25 to the aspirating pickup tube 18.

During operation of the aerosol generator, a supply of 'xerographicdeveloper powder particles 26 is positioned against meter blade 17. Themotor, when operated, causes rotation of disc 16 around its center byrotation of axle 22 causing rotation of axle 27 of the grooved disc.

The top surface of grooved disc 16 is uniformly grooved. As the groovesmove beneath the supply of developer powder particles 26, they becomeloaded with powder Meter blade 17 acts to meter a predetermined amountof particles to the surface of disc 16 as portions of the surface ofdisc 16 move beneath meter blade 17. Particles are then carried by therotating disc beneath aspirator tube 1?; where they are drawn up intopickup tube 18 and are carried to the output point of the aerosolgenerator.

The output of the aerosol generator is fed to a belt loading zone whichin this embodiment is shown as a cylinder designated 37. This cylindercomprises an enclosed but hollow cylinder having an open slot 39 at thetop and an entrance point at the base. The output tube of the generatorconnects to the entrance point at the base and conveys the createdaerosol from the aerosol generator to the interns of the cylinder. Atape of material 28 passes over the cylinder and thus over the slot andpowder from within the cylinder passes to the tape material as it leavesthe cylinder. It is to be realized that the belt loading zone couldcomprise a cylinder having more than one slot at the top. The tape issupplied from supply spool 34 and is carried to take-up spool 31. Thepath of tape 28 is from supply spool 30 over first guide rod 32, thenover first guide napping rod 33, then over tension rod 34 which operatesto position the belt against brush 40, then over second guide nappingrod 35, then beneath second guide rod 36, then over loading cylinder 37,then around drive capstan 38 to take-up spool 31. Napping brush is shownpositioned to contact tape or belt 28 and brush up a nap on the surfaceof the tape material at a point between first guide napping rod 33 andsecond guide napping rod 35. An exhaust duct 41 is positioned above theloading or coating cylinder 37 to pick up and convey away from themechanism the powder particles which pass through tape 28 at the pointof loading.

A motor is connected to drive capstan 38. Motor 21 illustrated in thisfigure may be used connected through gears or the like to cause rotationof drive capstan 38. The outer surface of capstan 38 is a roughenedsurface and the belt material is held in close contact thereto anddriven or caused to move when capstan 38 is rotated. A clutch mechanismmay also be inserted in the connection between capstan 38 and itsdriving motor 21 so that operation of the aerosol generating equipmentmay take place without operation of the tape loading mechanism. It is tobe realized, of course, that a separate motor may be used to drivecapstan 38. A motor may be used to cause napping brush 40 to rotate,and, as in the case of capstan 38, the driving motor may be motor 21 ora separate motor connected directly to napping brush 40. A frictionbraking mechanism is applied to the axle of supply spool 30 and aslipping drive friction clutch is applied to take-up spool or reel 31.The 'f'ri'ction slipping clutch and friction braking mechanism act tohold tape 28 taut while in position over the different guide rods andthe coating cylinder. The friction slipping clutch may be connectedbetween the axle of take-up reel 31 through gears to the motor operatingdrive capstan 38, or it may be driven by other driving means.

When the tape loading mechanism is operated, drive capstan 38 is causedto move at a uniform speed, thereby imparting uniform speed to the tapematerial. Although the speed of rotation of take-up reel 31 varies withthe amount of material already loaded to the spool, the takeup reel 31driven by a motor through a slipping clutch winds up as much material asis supplied to it. The braking mechanism on supply spool 30 allows onlythat much tape to unwind as is caused to unwind by the rotation ofcapstan 38. Supply spool 30 thereby allows a uniform amount of tapematerial to pass through the path provided for tape 28, although supplyspool 30 rotates at varying speeds depending on the amount of tape onthe spool. The napping brush 40 rotates in this embodiment against asurface of the tape, thereby imparting nap to the material. The nappedsurface of tape 28 is then carried in contact with coating cylinder 37and over the slot in cylinder 37. Means may also be inserted in acombination device to brush against and thereby impart nap to the othersurface of the tape. The powder output from the aerosol generatorcarried to coating cylinder 37 is blown into and through tape 28.Particles which pass through tape 28 at the point of coating arewithdrawn by exhaust duct 41 and the loaded or impregnated tape is woundup on take-up reel 31. p

The supply of gas supplied to the regulating valve through input tube 23in Figure 2 may be from any source of compressed or pressurized gas,such. as, for example, an air pump or like pressure generating memher,or a suitable pressurized gas container. Such containers are readilyavailable on the commercial market in the form of gas capsules of carbondioxide or the like under pressure, in the form of bombs or the like ofgas such as fiuoro-chloro-alkanes, which are available under the generalfamily name of Freon. Similarly, a suitable system may comprise a pumpor generating means optionally in combination with a pressure chamberwhereby fluctuations in pressure may be limited or avoided.

Reference is now had to Figure 3 wherein is shown a detailed view ofanother embodiment of a tape loading mechanism. A supply spool 42supplies the tape 43 for loading purposes. The tape passes over coatingcylinder 45 and then beneath drive capstan 46 to take-up reel 47. Amotor 4-8 is connected to drive capstan 46 causing rotation of capstan4-6 thereby imparting motion to tape 43. A supply of powder particles inan aerosol is supplied to input tube 50 and the particles are carriedalong the tube length and through coating cylinder 45 to the outputslots 44 at the top of cylinder 45 at which point particles areimpregnated into belt 43. A friction slipping clutch mechanism 49 causestake-up spool 47 to take up as much belt as is caused to move to it bythe rotation of capstan 46. A friction braking mechanism 51 on supplyspool 42 limits the freedom of rotation of this spool and allows onlythat much belt demanded by the rotation of capstan 46 against the beltmaterial to move from supply spool 42. Means other than the brakingmechanism 51 may be employed to hold the tape taut such as a fiat springto apply tension against the tape or other mechanism generally known tothose in the art.

In this figure the napping element or the napping brush, which appearedin Figure 2, does not appear. The tape or belt material used for loadingin this figure in one which either has been pretreated by napping or thelike or is one which does not need such pretreatment. Input tube 50 isfed with an aerosol of xerographic developer powder particles. Theaerosol could be created using a generator similar to the one shown inFigure 2, or other similar devices to create aerosols of powderparticles could be used.

For proper operation to produce uniformly loaded belts, it is desirableto supply a uniformly dense and uniformly constant aerosol of powderparticles to input tube 50. It is also desirable to cause belt 43 tomove at a uniform rate over the slots in coating cylinder 45. When theseelements are present, a uniform aerosol of powder particles isconstantly presented to a section of belt for loading purposes,resulting in a uniformly impregnated or loaded tape, ribbon, or belt ofmaterial which may then be used in generating aerosols of xerographicdeveloper powder particles.

Coating cylinder 45 is preferably a hollow cylinder having a smoothouter surface and at least two openings. One opening is needed for theinput tube. The other opening or openings comprise the output slot orslots. Smoothness of the outersurface is desirable so that as littleresistance to movement by belt 43 in contact with it as is possible isattained, thereby facilitating smooth movement by belt 43 at a uniformlinear speed. The cylinder acts as an expansion chamber and it ispresently believed that a pluralityof output slots makes for a moreuniform coating of the belt. The hollowness of the cylinder, also, it isbelieved, creates a type of swirling action of the powder particlespresented from the input tube 50, and this action tends to deagglomerateparticles before they are presented to the belt for loading purposes. Itis to be realized, however, that belts may be loaded directly withoutpassage of the aerosol through such an expansion chamber.

In impregnating or loading belts, it has been found that belt materialsaccept powder to a saturation point. Particles carried to the materialabove the saturation point or slightly past saturation adhere onlyslightly to the material and may be shaken loose.

To assure uniformity in belt loading, it is sometimes desirable to loadto saturation. This is so, for example, when uniformity in the output ofthe aerosol generator fed to the loading zone is questionable. It is tobe realized, however, that belts may be loaded well below the saturationpoint by passinga belt or tape through the loading zone at high enoughspeeds to avoid loading to the saturation point or by using a thinaerosol in impregnating thev belt material.

Using an automatic loading machine, it is possible to saturate the beltmaterial with powder particles by passing the belt through the aerosolone time or a number of times. More load per belt will naturally resultusing the same aerosol when the belt is passed through it at the samerate of speed a greater number of times. However, when belt saturationis reached, powder particles will tend to no longer form as part of thebelt material and although some particles may deposit on areas of thebelt, these particles may be removed to assure uni- 1ffirmity in loadthroughout by shaking the belt or the An important consideration informing belts for high quality xerographic reproduction is the beltmaterial itself. The material should be uniform throughout. This willassure presentation to the aerosol of powder particles, for loadingpurposes, of a material which is at all points able to hold the sameamount of particles and also a material which presents the sameresistance to the flow of the particles in the aerosol. The beltmaterial may be any porous material which will allow the gas of theaerosol to pass through. At the same time the material should beamaterial which will tend to hold particles by withdrawing them from theaerosol. A study has been made of various cloth and cloth-like materialsmaterial and scraping off any excess powder with a blade. The techniqueused is similar to the manual impregnation techniques mentionedpreviously in this application.

It is to be realized, however, that the data obtained are indicative ofdata obtainable when using automatic loading techniques, as have beendiscussed herein.

This table indicates that materials having considerable nap are mosteffective in holding powder. It is to be understood that the materialslisted in Table I are only a sample of materials which could be used toact as belt material for loading purposes as is being discussed herein.Any material capable of accepting and holding powder particles as powderparticles are blown to and through it is intended to be encompassedwithin the scope of this invention. For example, a treated mesh metalscreen has been found to work well and other similar materials exist andare intended to be encompassed herein.

Napped cotton flannel and equivalent materials are the preferredmaterials as belt material for loading purposes. It has been. foundthrough usage that the output when cotton flannel belt material is usedis highly constant, dense and uniform, and it is presently believedcotton flannel or equivalent materials accept a dense and highly uniformload. An equivalent material for cotton flannel would be cotton tape orbias material with a napped surface or napped surfaces. Therepresentation in Figure 2 of a napping brush is intended to convey amethod for putting a nap on the surface of cotton tape or bias material,but it is to be realized that other mechanisms for accomplishing thisobjective are intended to beencompassed by this invention.

Although a particular aerosol generator has been shown in Figure 2,there is no intention to limit this invention to that particulargenerator. The generator included therein is for purposes ofillustrating a compact unit including the aerosol generator and the tapeloading mechanism, and it is to be realized that other aerosolgenerators are intended to be included in this invention.

A number of aerosol generators exist and are known generally to the art.One such generator, for example, comprises an endless belt positionedwithin a housing. A supply of developer powder particles is positionedat the base of the housing and the endless belt is caused to movethrough the supply of powder particles. The belt is next led followingmovement through the particles to an output tube. At the point of theoutput tube the belt is drawn tautly over the internal opening of theoutput tube, and gas moving through the housing moves through the beltcarrying powder particles, thereby creating at the output end of thedevice an aerosol of xerographic developer powder particles. Anothertype of powder cloud generator which may be used to create the aerosolof xerographic developer powder particles to feed to the tape loadingmechanism comprises a housing enclosing a disc on which is positioned asupply of developer powder particles. A blade holds the supply ofdeveloper powder particles in place and the disc is rotated beneath thepowder particles. The blade meters a uniform amount of powder particlesto areas of the disc passing therebeneath. The metered supply of powderparticles is then carried to an area where the output is created. In onetype of generator, the output is taken from the housing by gas rushingfrom within the housing through the disc flow at the loading zone.

and through the tubes supplying the aerosol of powder and into an outputtube pressed firmly against the disc material. In another case, theoutput tube is positioned slightly above the disc and as gas from withinthe housing rushes out the output tube, it entrains the powder particlespositioned on the disc beneath the output opening. The output fromeither of these last two generators could be fed to a tape loadingmechanism as illustrated in Figure 3 and in Figure 2 for purposes ofimpregnating or loading tape or belt material. It is to be realized thatit is not intended to limit this invention to the generators discussedabove or the generator shown in Figure 2. These generators have beendiscussed for illustrative purposes, and it is intended to includewithin this invention the many possible mechanisms and means forgenerating aerosols of powder particles which may be fed to the tapeloading mechanism.

From the point of view of composition of the developer particles in theaerosol fed to the tape or belt material for loading, prints or picturesmay be produced with belts or tapes loaded or impregnated with charcoal,carbon blacks, or carbonaceous pigments. Under proper conditions, any ofa number of various carbon or lamp black materials may be employed,including such material as furnace blacks, channel blacks, and the like.In addition, there may be used such material as milled charcoals andsimilar materials, or, if desired, finely divided materials having addedpigment matter. In the latter category are materials such as finelydivided resins containing pigments or dyes such as carbonaceous pigmentsor various coloring pigments and the like, compositions of this typebeing preferred where the print or picture ultimately is to be madePermanent by a fusing process including heat or vapor fusing. Forhighest quality work the presently preferred material is milled woodcharcoal.

A number of generalities apply in carrying out this invention. Forexample, aerosols of powder particles of different densities may beefficiently used in loading tapes and in creating impregnated beltsaccording to this invention. If a particular load in a belt is desired,such a load may be attained either when using a thin aerosol or a verydense aerosol. Other means of control exist. For example, the belt ortape may be made to move over the loading cylinder at a rapid pace or aslow pace. This may be accomplished through the use of a variable speeddriving motor. Also, it is possible to reload a loaded belt. This factis pertinent, in that if a particular linear speed of movement of thetape material is desired, a particular load may be attained by cyclingthe belt or tape material over the loading zone one or many times,depending upon the aerosol of powder particles being supplied to thebelt material.

Another generality relates to air flow at the loading zone and pressuresthrough the generator system and to and through the input tube of thetape loading mechanism. The desire is to produce an aerosol which willimpregnate or load a tape or belt of material. When too high an air fiowis used, insufficient loading of belt or tape materials results. Whentoo low an air flow is used, the tendency again is for partial andinefiicient loading to take place. Particles in such an instance are notblown throughout the thickness of the belt, but tend to stop as theystrike the cloth. However, uniformity in density of cloud presented tothe belt will produce a uniformly loaded belt of material. Good beltshave been obtained using air flows at the loading zone ranging from .1c.f.m. to 25 c.f.rn., free air flow, and belt loading will result usinga broader range of free air The pressure of the system particles to thetape loading mechanism may also vary substantially. A general range forgood loading is from to 4 psi, but it is to be realized that a broaderrange than this may be used and valuable results will still be 'obtainedfor use in the xerographic art.

The linear speed of the tape may also vary within a substantially largerange. Very good results for high quality prints are obtained whenloading with a proper aerosol at anywhere from .08 inch per second to 4inches per second linear speed of the tape. However, good quality printsmay be obtained from tapes which have been loaded within a substantiallybroader range. For example, it is believed a tape can be loaded atinches per second.

In the preferred embodiment of this invention, developer particles aresupplied mixed in air to the loading apparatus under a pressure of 4psi. at a rate of 1 /2 cubic feet per minute, carrying in the mixture1.3 grams per cubic foot of gas. The belt is loaded at a rate of 1 footper minute and when loaded is impregnated with mgms. of developer powderper foot of belt when the width of the loaded area is /2 inch. Theparticular belt material in this embodiment is white medium weightcotton flannel 4 ounces per square yard. The amount of powderimpregnated into the belt is approximately of the powder flowing to thebelt loading apparatus. The other 95% is spent by remaining in the tubeand the cylinder and by being dispersed in air after passing through thebelt. In use, four inches of belt loaded as per the preferred embodimentis required to develop a fine grain high quality picture on a 4 x 5plate.

A loaded or impregnated belt is presently believed to have powderextending through all areas of thickness of the belt material. The loadaccepted by each belt is dependent on the density of the cloth and theability of the cloth to load with powder particles. By ability of thecloth to load it is intended to include such elements as the effect ofthe cloths mesh and the cloths nap, whereas the density is intended toinclude the effect of such elements as the thickness of the cloth.Powder loaded or impregnated to the belt deposits both between thethreads and on threads and between areas of napped material and on thenapped material. Belt materials, it is presently believed, have asaturation point above which they tend not to accept within themselvesany more developer powder particles. Although powder particles may befed to the belt material and although such particles may occasionallyremain resting on the surface, they are easily removed by simply shakingthe loaded belt. Thus, it is believed that particles above thesaturation point of the belt will shake loose; whereas those particlesbelow the saturation point which have become part of the belt materialwill remain adhering to'the belt material.

Belts described according to this invention, when used in powder cloudgenerators, have the advantage of consistency and uniformity betweenbelts with similar characteristics. Two belts of similar material loadedwith a similar aerosol at the same rate of speed will produce highlyconsistent and uniform cloud outputs when used in similar powder cloudgenerators. Also, it has been found that since belts tend to stoploading at what is believed to be a saturation point, the aerosol fed tothe belt or tape material need not be highly uniform, and yet a beltwill be produced which when used with a powder cloud generator willdeliver a consistent and uniform aerosol of powder particles. Belts alsohave the advantage of being able to produce fine and high qualityaerosols of xerographic developer powder particles which may be useddirectly for development purposes without other elements between thepowder cloud generator and the development zone such as settlingchambers or the like. Another advantage of belts loaded according tothis invention is that they are compact and also they may be stored,producing convenient sources of powder for powder cloud generators to becalled upon when needed.

While the present invention as to its objects'and advantages, as hasbeen described herein, hasbeen carried out in specific embodimentsthereof, it is not desired 9 to be limited thereby, but is intended tocover the invention broadly within the spirit and scope of the appendedclaims.

What is claimed is:

l. A device to impregnate tapes with releasable xerographic powderparticles comprising a powder cloud generator for creating an aerosol ofxerographic developer powder particles, a hollow enclosed cylinder, apowder cloud conduit connecting said powder cloud generator to saidcylinder, a longitudinal slot opening in said cylinder to provide anexit for said powder particles from said cylinder, and tape transportmeans positioned and adapted to uniformly move a permeable napped tapematerial past said slot and in contact with and transversely coveringsaid slot while the aerosol of xerographic developer issues from saidslot.

2. A device to impregnate tapes with releasable xerographic powderparticles comprising a powder cloud generator for creating an aerosol ofxerograp-hic developer power particles, a hollow enclosed cylinder, apowder cloud conduit connecting said powder cloud generator to saidcylinder, a longitudinal slot opening in said cylinder to provide anexit from said cylinder for said powder particles, tape transport meanspositioned and adapted to uniformly move a permeable napped tapematerial past said slot and in contact with and transversely coveringsaid slot while the aerosol of xerographic developer issues from saidslot, and napping means positioned with respect to said transport meansto impart a surface nap to the surface of said tape which moves intosurface contact with said cylinder before said tape passes across saidslot.

References Cited in the file of this patent UNITED STATES PATENTS1,713,746 Dennison May 21, 1929 2,309,981 Randall Feb. 2, 1943 2,416,695lessop et a1. Mar. 4, 1947 2,532,298 Goldstein Dec. 5, 1950 2,614,655Katz Oct. 21, 1952 2,725,304 Landrigan et a1 Nov. 29, 1955 2,750,921Purdy June 19, 1956 2,792,971 Kaiser May 21, 1957 2,824,812 Fauser eta1. Feb. 25, 1958

